1. Field of the Invention
The invention relates to embossed rolled steel sheet. More specifically, the invention relates to embossed rolled steel sheet with a surface pattern that replicates an abrasively polished surface along with a method and apparatus for producing the same.
2. Description of the Prior Art
A significant portion of the flat rolled stainless steel sheet used commercially has a polished finish. The finish is generally produced by abrading the surface to produce a sanded appearance. This sanded appearance may also be produced by embossing on the steel sheet a similar pattern. While embossing generally provides the visual equivalent of the abraded surface, a relatively small percentage of steel sheet is processed in this fashion to produce such a surface.
However, abrasive finishing is costly and time-consuming and may produce an inconsistent surface that is prone to defects, such as polishing chatter, pits, and abrasive belt marks.
FIG. 1 illustrates a section of steel sheet 10 having a surface 15 with a sanded appearance. The surface 15 includes a multiplicity of slits 20 oriented about a longitudinal axis 25 generally in a random fashion.
As seen in FIG. 2, the slits (not shown) on the surface 15 of the sheet 10 are produced by moving the sheet 10 in a direction 30 from a payoff reel 32 past an abrasive roller 35 which has abrasive tape 40 about the periphery of the roller 35 to a take-up reel 37. A relatively rigid roller 45 opposes the roller 35, thereby permitting the abrasive tape 40 of the roller 35 to be applied against the sheet 10 with a predetermined pressure. Furthermore, the roller 35 rotates as indicated by arrow 47 against the direction 30 of travel of the sheet 10 by a motor 50 and a connecting belt 55.
The surface 15 of the sheet 10 contacts the roller 35 only tangentially such that rotation of the roller 35 against the surface 15 produces the short slits 20 found in FIG. 1. In general, the length of these slits along the longitudinal axis 25 is between 5 to 10 millimeters and these slits are unevenly spaced since they correspond with the locations of the individual pieces of grit on the abrasive tape 40.
While this surface finish is aesthetically pleasing, in the event a portion of the surface becomes damaged, once repaired the sanded appearance must be reproduced. It is extremely difficult to reproduce this appearance because of the randomly spaced longitudinal slots 20 and it is equally difficult to provide a seamless transition between the repaired surface and the original surface. For that reason, a different type of surface finish was sought that would be more amenable to being repaired.
FIG. 3 illustrates a portion of a steel sheet 110 having a surface 115 with a plurality of grooves 120 extending parallel to a longitudinal axis 125.
As illustrated in FIG. 4, the grooves 120 in the surface 115 of the sheet 110 are produced by moving the sheet 110 in the direction of arrow 130 from a payoff reel 132 between an element 135 having an abrasive surface 140 and a rigid roller 145 opposing the element 135 to a take-up reel 147. The abrasive surface 140 extends across the entire width of the sheet 110 such that when the sheet 110 is moved in the direction 130, the plurality of grooves 120 is produced over the surface 115 of the sheet 110.
This surface finish is more amenable to being repaired; however, as previously mentioned, abrasive finishing is costly and time-consuming and may produce an inconsistent surface with defects. As an example, FIG. 5, which is an optical microscopy image of a steel sheet of stainless steel type 304 having an AISI number 3 polished finish to give the appearance of a brushed finish, illustrates typical surface tears and pits, not uncommon when abrasive polishing is used.
Steel sheet surfaces with these defects have associated disadvantages. First of all, the exposed steel sheet with surface tears and pits is more prone to corrosion than a surface without these. Furthermore, polished steel sheet is used on equipment in contact with food, chemicals and pharmaceuticals because of its resistance to corrosion and oxidation. It is important for the surface finish to be aesthetically pleasing, cleanable and resistant to corrosion. The cleanability of the sheet is significantly reduced by the introduction of such defects. Furthermore, as highlighted in the discussion of FIG. 4, the abrasive surface 140 is urged against the surface 115 of the sheet 110 and therefore a typical abrasive element 135 must be replaced approximately every 5,000 feet of surface that is abraded. Finally, the speed at which the sheet 110 travels past the abrasive element 140 is generally approximately 50 feet per minute. This produces a bottleneck since, for the most part, all of the other processes associated with finishing the sheet run at much higher speeds.
For that reason, a sheet is desired with a surface pattern that provides the same relative ease of repair to damage on the brushed surface but does not have the disadvantages associated with the damage caused by abrasion, relatively short life of the abrasive element and relatively slow speed associated with the abrasion process.